The argument is complicated and concerns polonium halos. It is very difficult, if not impossible, for the non-scientist to analyze or evaluate.

I cover the argument a bit deeper on my Robert Gentry page, but it seemed best to just give this simple report here.

Polonium Halos: The Simple Version

Polonium halos

The picture to the right is of polonium halos in granite. They are caused by polonium-218 breaking down through a series of steps into lead-206.

These rings, formed by that kind of radioactive decay, takes only about a half hour to happen. This is not anywhere near enough time for magma to cool and become granite. Thus, somehow, this granite appears to have appeared without any cooling.

Instant creation? A young earth?

The source for Dr. Gentry's granite is unknown, so no one can actually go examine what happened. It's like a crime scene that can't be searched. Still, there's the granite, and there are the halos.

The only argument against Dr. Gentry's claim that made any sense to me was the argument that the polonium was produced from the decay of uranium. The scientist making the argument says that the uranium decayed—over a period of millions of years—into radon. Radon is a gas. It moved through fissures in the rock, decayed to polonium, and the polonium then produced the halos long after the granite cooled.

On the other hand, response to a published article is what peer review is all about. "The Age of the Earth- Creationism and Accelerated Decay Rates" (http://orgs.usd.edu/esci/age/content/creationism_and_young_earth/accelerated_decay.html, which was up Aug. 1, 2013 but apparently is not now) on the University of South Dakota web site, gives a similar explanation:

The accepted scientific model actually does a good job of explaining these halos. Given that almost all of uranium-238's 4.5 billion year half life results from the first step in its decay series where 238U decays to 234Th, plenty of uranium would still exist long after slow-cooling magma had solidified. After several more steps, the thorium would eventually decay to radon, which is a noble gas. Noble gases are considered slippery because they do not latch onto other isotopes; that could allow the radon to travel the small distances and create the gaps between the halos that the RATE team noted.

For those that really enjoy researching these kinds of things, RATE (Radioisotopes and the Age of The Earth) answered one response to Gentry's polonium halos.

Their response doesn't really address the radon issue discussed in the quote in the text box above. They write:

Isaac made the statement that “the presence of uranium also seems to provide a reasonable explanation for the source of the polonium and polonium halos with normal decay rates and standard ages of granite” (p. 144). He apparently does not recognize that below the annealing temperature of 150°C, hydrothermal convective systems can only last for a short time. Laboratory observations show that water below that temperature will flow through the biotite for only a few months, certainly not for millions of years. Uniformitarian rates of decay in a uranium halo fall vastly short of producing the hundreds of millions of water-transported polonium atoms needed to make a fully-developed polonium halo, particularly for polonium-214 and polonium- 218 radiohalos.

Perhaps, but the argument is that tiny atoms of radon, created by the uranium over geologic time, would migrate through the granite to produce the polonium necessary for the haloes. So this doesn't even address, much less answer, the alternative method suggested.